The present application hereby claims priority under 35 U.S.C. xc2xa7119 on German patent publication number DE 10127357.6 filed Jun. 6, 2001, the entire contents of which are hereby incorporated by reference.
The invention generally relates to a method and a device for patterning printed circuit boards. Preferably, the circuit boards are ones with coarse conductor structures and with at least one region with fine conductor structures. A metal layer may be applied to an electrically insulating substrate and the desired conductor structure may be exposed from this metal layer by partial etching.
EP 0 062 300 A2 has already disclosed a method for manufacturing printed circuit boards in which a metallic etch resist is applied over all the surface of a metal layer, and is selectively removed again in the areas which do not correspond to the conductor structures using laser irradiation. The conductor structures are then formed by etching away the metal layer which is exposed in this way.
DE 41 31 065 A1 also discloses a method for manufacturing printed circuit boards in which a metal layer and a metallic or organic etch resist layer are applied in succession to a substrate, after which this etch resist layer is removed using laser irradiation in the regions which directly adjoin the later conductor track pattern. The metal layer which is exposed as a result, is etched away in such a way that the conductor track pattern, and islands of the metal layer on the substrate, which are electrically insulated from the pattern by etched trenches, remain. The patterning using laser irradiation can be performed quickly because the regions of the etch resist layer to be removed only have to have a small width and the relatively large surfaces between two conductor tracks are left.
WO 00/04750 A1 also describes a method for manufacturing coarse conductor structures and fine conductor structures in which an etch resist is patterned in the region of the coarse conductor structures via photolithography, while an etch resist is patterned in the region of the fine conductor structures using a laser beam. The etch resist layers which are thus patterned in various ways are then etched in a known fashion. Although the possibility of operating with the same etch resist for the various patterning methods and of etching both the coarse and the fine conductor structures in one operation are mentioned in the publication, an optimum operating sequence is not obtained here because the metallic etch resist (for example tin) which is generally used for the laser patterning is less suitable for the photolithographic method.
The object of an embodiment of the present invention is to specify a method and a device with which printed circuit boards with coarse and fine conductor structures can be patterned in as simple and economical way as possible. According to an embodiment of the invention, this object can be achieved with the following method steps:
a) applying a metal layer to an electrically insulating substrate,
b) applying an etch resist layer to the metal layer,
c) exposing the contours (62) of the envisaged coarse conductor structures (31) by partially eroding the etch resist layer (61) with a first laser beam (14) with a predefined first wavelength and a first processing field size (3) which is predefined by a first imaging unit (13),
d) exposing the contours (63) of the fine conductor structures by partially eroding the etch resist layer (61) with a second laser beam (24) with a predefined second wavelength and a second processing field size (4) which is predefined by a second imaging unit (23), the second wavelength being shorter than the first wavelength and/or the second field size (4) being smaller than the first field size (3),
e) producing the coarse and the fine conductor structures (31, 41) simultaneously by etching the exposed metal regions (62, 63), and
f) exposing the surfaces of the conductor structures by eroding the rest of the etch resist layer.
An embodiment of the invention is therefore concerned with producing both coarse and fine conductor structures with similar method steps, specifically by patterning an etch resist layer and subsequently etching, but allowing for different conductor structures and correspondingly different insulating spacings by the selection of different lasers. In doing so, a better processing speed for the respective structure is achieved. In this regard, an embodiment of the invention makes use of the realization that a laser beam with a short wavelength and a short focal length can produce fine structures with precision in a small processing field, but is too slow for an economic method of operation for processing relatively wide structures and relatively large fields, while a laser beam with a long wavelength and a setting to a large focal length can process relatively wide structures in a large processing field at a considerably higher speed.
In one advantageous embodiment of the method according to the invention, there is provision that, for the processing of the coarse conductor structures, the first laser has a wavelength between 1064 nm and 355 nm, preferably 1064 nm, and the second laser has a wavelength between 532 and 266 nm, preferably 532 or 355 nm, the wavelength of the first laser being in all cases greater than that of the second laser. Furthermore, in the preferred refinement of the method according to an embodiment of the invention there is provision for the beam of the first laser to be focussed over a larger focal length than the beam of the second laser. As a result of this, the first laser passes over a larger processing area than the second laser.
A device according to an embodiment of the invention for patterning printed circuit boards with coarse conductor structures and with at least one region with fine conductor structures has the following features:
a) a support for positioning a printed circuit board,
b) a first laser with a deflection optical device and an imaging unit with a first focal length which can be positioned over the surface of the printed circuit board in such a way that it is capable of irradiating a first processing field size,
c) a second laser with a deflection optical device and an imaging unit with a second focal length which is capable of irradiating a second processing field size, the second laser having a longer wavelength than the first laser, and/or the second focal length and the second field size being smaller than the first focal length and the first field size, and
d) a control device for respectively irradiating large fields of the printed circuit board with coarse conductor structures using the first laser and relatively small fields of the printed circuit board with relatively fine conductor structures using the second laser.